and the next figures compare working cost of various power-
COMPARATIVE COST OF ONE I.H.'P. HR.
Steam ... ... \d.
(Lighting) . \d. to \d.
\d. or less.
Petroleum ... ... \d.
Electricity (from main) ... 2d.
Hydraulics (from main)... i\d.
P. 7<9p. Oil Engines.—For motor-cars the Priestman
•engine was too heavy, so Daimler and others designed lighter forms,
Fig. 878. There were two cylinders, side by side, having cranks
at 180°, and using the Otto cycle, so there was an explosion per
revolution. The charge of oil-vapour and air entered at A, the
exhaust leaving at B ; and the ignition tube c, of platinum, was
kept hot with a lamp. The oil, benzoline, flowed from reservoir
R through the chamber r>, at a slow and regular rate, controlled
by float E, and as it emerged at F was wafted into spray by the
suction air at a The exhaust-valve B was lifted every second
revolution by a cam j, worked from crank shaft by gearing.
Further information on motor-cars and their details is given in
the Appendices at pp. 947, 965, 999, and 1182.
Hot-air Engines.—These are sufficiently illustrated by the